CHICAGO (Reuters) - Scientists hope they've figured out a way to trick plants into doing the dirty work of environmental cleanup, U.S. and British researchers said on Monday.

"Our work is in the beginning stages, but it holds great promise," said Sharon Doty, an assistant professor of forest resources at the University of Washington, whose study appears in the Proceedings of the National Academy of Sciences.

In work they describe as preliminary, researchers at the University of Washington say they've genetically altered poplar trees to pull toxins out of contaminated ground water, perhaps offering a cost-effective way of cleaning up environmental pollutants.

A group of British researchers, meanwhile, has developed genetically altered plants that, they say can clean residues of military explosives from the environment.

Doty's research is part of an emerging area of study known as phytoremediation, which aims to use trees, grasses and other plans to remove hazardous materials.

"Phytoremediation is basically a solar-powered pollutant-removal system," said Doty in comments e-mailed to Reuters.

Using plants to do environmental cleanup is more than 10 times cheaper than other technologies. It is also less intrusive and more aesthetically pleasing, she said.

Genetically modified poplar trees in Doty's lab sucked 91 percent of the toxin trichloroethylene from a liquid solution. Natural plants were only able to remove 3 percent of the toxin, which is the most common ground water contaminant in the United States. What remains unknown, is how these genetically altered organisms interact, short and long term with the rest of the ecosystem, including animals and humans.

The genetically modified plants in the study were grown in vials and were just several inches tall. But these tiny plants were able to metabolize the pollutant into harmless byproducts 100 times faster than the natural plants.

Researchers at the University of York, meanwhile, devised genetically modified plants using genes from microbes that can degrade the explosive RDX, a potential cancer-causing agent.

To test their system, they introduced genes into Arabidopsis plants -- the plant equivalent of lab rats.

"The studies here illustrate that these genes ... could be engineered into plant species suited to growth on military training ranges and used to remediate RDX," the authors wrote.

As with genetically modified foods, many experts deem genetically modified plants as a potential threat, and relatively untested in ecosystems, where GMO organisms can have potentially a significant impact.

Doty and colleagues, for example, chose poplars because they are fast-growing and can grow for several years without flowering -- allowing time for them to be harvested before they develop seeds.

Because of these concerns, she said these efforts would be limited to carefully monitored government cleanup sites under the Environmental Protection Agency's 1980 "Superfund law," which was created to address hazardous and toxic chemical spills.

Of course, naturally occurring plants can do the work as well, but they are too slow. And she said intensive, expensive engineering methods are often abandoned.

"We need a faster, less expensive method to remove carcinogenic pollutants from the environment so they will no longer be ignored," she said.